A vehicle often requires knowledge of its environment. This may be accomplished by integrating information derived from multiple onboard navigation sensors, such as a GPS (Global Positioning System) receiver, an IMU (Inertial Measurement Unit), an altimeter, etc. Using such sensors, the vehicle may obtain its own position, velocity and acceleration information. Information of obstacles in the path of the vehicle may also be obtained using onboard target tracking sensors to derive position and bearing information of targets proximate to the vehicle.
By optimally integrating navigation sensors and target tracking sensors, guidance laws may be used to generate a desired trajectory for the vehicle.
Generally, target tracking sensors produce range measurements of a target with respect to the vehicle by using an active sensor, such as a radio or acoustic radar or a laser range finder. The operation of an active sensor depends on measurement of the traveling time between the transmitted signal and the received reflected signal.
In various scenarios it is desirable to maneuver unmanned aerial vehicles (UAVs) into areas for surveillance and reconnaissance. One scenario may include a low flying UAV with hover capability, navigating through a wooded area under a tree canopy. Another scenario may include a UAV with hover capability, navigating in a cave and sharply maneuvering to avoid collision with a wall. Providing autonomous collision avoidance for such a UAV is desirable by using an onboard camera having intensified video.
One advantage of using an intensified camera is the ability to gate the intensifier. Gating provides a mechanism to gather range information that may be used to form spatial three-dimensional (3D) knowledge about a region the vehicle is maneuvering through. Potential collision obstacles may be located, relative to the sensor, within the 3D space-of-regard.
When attempting to traverse a space where obstacles prevent a straight-line path, the limiting factor becomes the accuracy with which objects may be located. A range-gated camera may be used with extremely narrow range gates to locate objects in the space. This approach fails, however, if the spatial separation between obstructions becomes less than the illuminator pulse width, times one half the speed of light. In a scenario of a UAV navigating through a wooded area or a cave, the separation between obstructions may be on the order of 2 feet, thus requiring an illuminator pulse of less than five nanoseconds (ns). Acquisition of a small, low cost illuminator with a pulse width this short, and with enough intensity to generate a usable image, presents a major hurdle in developing a low cost UAV with collision avoidance. A different approach is, therefore, needed.
The present invention addresses a collision avoidance system using a gated camera sensor, which does not require the illuminator to be high performance.